Re: [PATCH v2 1/3] am: add --show-current-patch

[Junio C Hamano]

Duy Nguyen  writes:

> Subject: [PATCH] Preserve errno in case case before calling sth_errno()
>
> All these locations do something like this
>
> sth_errno(..., somefunc(...));
>
> where somefunc() can potentially change errno, which will be read by
> sth_errno(). Call somefunc separately with errno preserved to avoid
> this.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy 
> ---
>  builtin/am.c  |  8 +++-
>  builtin/commit.c  |  8 ++--
>  builtin/init-db.c |  9 ++---
>  rerere.c  |  9 ++---
>  shallow.c | 27 ++-
>  5 files changed, 43 insertions(+), 18 deletions(-)

> diff --git a/builtin/init-db.c b/builtin/init-db.c
> index c9b7946bad..e384749f73 100644
> --- a/builtin/init-db.c
> +++ b/builtin/init-db.c
> @@ -570,9 +570,12 @@ int cmd_init_db(int argc, const char **argv, const char 
> *prefix)
>   set_git_work_tree(work_tree);
>   else
>   set_git_work_tree(git_work_tree_cfg);
> - if (access(get_git_work_tree(), X_OK))
> - die_errno (_("Cannot access work tree '%s'"),
> -get_git_work_tree());
> + if (access(get_git_work_tree(), X_OK)) {
> + int saved_errno = errno;
> + const char *path = get_git_work_tree();
> + errno = saved_errno;
> + die_errno(_("Cannot access work tree '%s'"), path);
> + }
>   }

This one is the most faithful conversion from "mechanical rewrite"
point of view, but I wonder if we should instead take the returned
path from get_git_work_tree() and use it in both calls.  After all,
this is hardly performance sensitive codepath, so even "an obviously
safe but wasteful with extra xstrdup/free" version

work_tree_path = xstrdup(get_git_work_tree());
if (access(work_tree_path, X_OK))
die_errno(_("msg..."), work_tree_path);
free(work_tree_path);

may be an improvement.

> diff --git a/rerere.c b/rerere.c
> index 1ce440f4bb..f19a53ff2c 100644
> --- a/rerere.c
> +++ b/rerere.c
> @@ -683,9 +683,12 @@ static int merge(const struct rerere_id *id, const char 
> *path)
>* A successful replay of recorded resolution.
>* Mark that "postimage" was used to help gc.
>*/
> - if (utime(rerere_path(id, "postimage"), NULL) < 0)
> - warning_errno("failed utime() on %s",
> -   rerere_path(id, "postimage"));
> + if (utime(rerere_path(id, "postimage"), NULL) < 0) {
> + int saved_errno = errno;
> + const char *path = rerere_path(id, "postimage");
> + errno = saved_errno;
> + warning_errno("failed utime() on %s", path);
> + }

Likewise.

> diff --git a/shallow.c b/shallow.c
> index df4d44ea7a..9da82f5292 100644
> --- a/shallow.c
> +++ b/shallow.c
> @@ -295,9 +295,12 @@ const char *setup_temporary_shallow(const struct 
> oid_array *extra)
>   temp = xmks_tempfile(git_path("shallow_XX"));
>  
>   if (write_in_full(temp->fd, sb.buf, sb.len) < 0 ||
> - close_tempfile_gently(temp) < 0)
> - die_errno("failed to write to %s",
> -   get_tempfile_path(temp));
> + close_tempfile_gently(temp) < 0) {
> + int saved_errno = errno;
> + const char *path = get_tempfile_path(temp);
> + errno = saved_errno;
> + die_errno("failed to write to %s", path);
> + }

It feels a bit questionable to my taste to pretend that we are truly
oblivious to how trivial get_tempfile_path() is, i.e. no more than
just a few field accesses to "tempfile" struct.  It buries more
important thing that is happening in the code in noise.

> @@ -319,9 +322,12 @@ void setup_alternate_shallow(struct lock_file 
> *shallow_lock,

Likewise.

> @@ -366,9 +372,12 @@ void prune_shallow(int show_only)

Likewise.

All others I snipped looked like good changes.  Thanks.

Re: [PATCH v2 1/3] am: add --show-current-patch

[Duy Nguyen]

On Fri, Feb 2, 2018 at 4:46 PM, Eric Sunshine  wrote:
> On Fri, Feb 2, 2018 at 4:25 AM, Duy Nguyen  wrote:
>> On Wed, Jan 31, 2018 at 02:59:32PM -0800, Junio C Hamano wrote:
>>> Eric Sunshine  writes:
>>> > On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy  
>>> > wrote:
>>> >> +   len = strbuf_read_file(, am_path(state, msgnum(state)), 0);
>>> >> +   if (len < 0)
>>> >> +   die_errno(_("failed to read '%s'"),
>>> >> + am_path(state, msgnum(state)));
>>> >
>>> > Isn't this am_path() invocation inside die_errno() likely to clobber
>>> > the 'errno' from strbuf_read_file() which you want to be reporting?
>>> True.
>>
>> Thanks both. Good catch. Of course I will fix this in the re-roll, but
>> should we also do something for the current code base with the
>> following patch?
>>
>> -   die_errno(_("could not read '%s'"), am_path(state, file));
>> +   saved_errno = errno;
>> +   path = am_path(state, file);
>> +   errno = saved_errno;
>> +   die_errno(_("could not read '%s'"), path);
>
> Rather than worrying about catching these at review time, I had been
> thinking about a solution which automates it using variadic macros.
> Something like:
>
> #define die_errno(...) do { \
> int saved_errno_ = errno; \
> die_errno_(saved_errno_, __VA_ARGS__); \
> } while (0);

That would be best. Unfortunately we have HAVE_VARIADIC_MACROS so we
need to deal with no variadic macro support too.
-- 
Duy

Re: [PATCH v2 1/3] am: add --show-current-patch

[Eric Sunshine]

On Fri, Feb 2, 2018 at 4:25 AM, Duy Nguyen  wrote:
> On Wed, Jan 31, 2018 at 02:59:32PM -0800, Junio C Hamano wrote:
>> Eric Sunshine  writes:
>> > On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy  
>> > wrote:
>> >> +   len = strbuf_read_file(, am_path(state, msgnum(state)), 0);
>> >> +   if (len < 0)
>> >> +   die_errno(_("failed to read '%s'"),
>> >> + am_path(state, msgnum(state)));
>> >
>> > Isn't this am_path() invocation inside die_errno() likely to clobber
>> > the 'errno' from strbuf_read_file() which you want to be reporting?
>> True.
>
> Thanks both. Good catch. Of course I will fix this in the re-roll, but
> should we also do something for the current code base with the
> following patch?
>
> -   die_errno(_("could not read '%s'"), am_path(state, file));
> +   saved_errno = errno;
> +   path = am_path(state, file);
> +   errno = saved_errno;
> +   die_errno(_("could not read '%s'"), path);

Rather than worrying about catching these at review time, I had been
thinking about a solution which automates it using variadic macros.
Something like:

#define die_errno(...) do { \
int saved_errno_ = errno; \
die_errno_(saved_errno_, __VA_ARGS__); \
} while (0);

Re: [PATCH v2 1/3] am: add --show-current-patch

[Duy Nguyen]

On Wed, Jan 31, 2018 at 02:59:32PM -0800, Junio C Hamano wrote:
> Eric Sunshine  writes:
> 
> > On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy  
> > wrote:
> >> Pointing the user to $GIT_DIR/rebase-apply may encourage them to mess
> >> around in there, which is not a good thing. With this, the user does
> >> not have to keep the path around somewhere (because after a couple of
> >> commands, the path may be out of scrollback buffer) when they need to
> >> look at the patch.
> >>
> >> Signed-off-by: Nguyễn Thái Ngọc Duy 
> >> ---
> >> diff --git a/builtin/am.c b/builtin/am.c
> >> @@ -2121,6 +2120,22 @@ static void am_abort(struct am_state *state)
> >> +static int show_patch(struct am_state *state)
> >> +{
> >> +   struct strbuf sb = STRBUF_INIT;
> >> +   int len;
> >> +
> >> +   len = strbuf_read_file(, am_path(state, msgnum(state)), 0);
> >> +   if (len < 0)
> >> +   die_errno(_("failed to read '%s'"),
> >> + am_path(state, msgnum(state)));
> >
> > Isn't this am_path() invocation inside die_errno() likely to clobber
> > the 'errno' from strbuf_read_file() which you want to be reporting?
> 
> True.

Thanks both. Good catch. Of course I will fix this in the re-roll, but
should we also do something for the current code base with the
following patch?

I think this is something coccinelle can help catch, but my
coccinelle-foo is way too low to come up with something like
"die_errno() must not take any arguments as function calls, except _()
and N_()".

-- 8< --
Subject: [PATCH] Preserve errno in case case before calling sth_errno()

All these locations do something like this

sth_errno(..., somefunc(...));

where somefunc() can potentially change errno, which will be read by
sth_errno(). Call somefunc separately with errno preserved to avoid
this.

Signed-off-by: Nguyễn Thái Ngọc Duy 
---
 builtin/am.c  |  8 +++-
 builtin/commit.c  |  8 ++--
 builtin/init-db.c |  9 ++---
 rerere.c  |  9 ++---
 shallow.c | 27 ++-
 5 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/builtin/am.c b/builtin/am.c
index acfe9d3c8c..ba67e187a4 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -244,6 +244,9 @@ static int am_in_progress(const struct am_state *state)
 static int read_state_file(struct strbuf *sb, const struct am_state *state,
const char *file, int trim)
 {
+   int saved_errno;
+   const char *path;
+
strbuf_reset(sb);
 
if (strbuf_read_file(sb, am_path(state, file), 0) >= 0) {
@@ -256,7 +259,10 @@ static int read_state_file(struct strbuf *sb, const struct 
am_state *state,
if (errno == ENOENT)
return -1;
 
-   die_errno(_("could not read '%s'"), am_path(state, file));
+   saved_errno = errno;
+   path = am_path(state, file);
+   errno = saved_errno;
+   die_errno(_("could not read '%s'"), path);
 }
 
 /**
diff --git a/builtin/commit.c b/builtin/commit.c
index 4610e3d8e3..39836b3734 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -780,8 +780,12 @@ static int prepare_to_commit(const char *index_file, const 
char *prefix,
}
 
s->fp = fopen_for_writing(git_path_commit_editmsg());
-   if (s->fp == NULL)
-   die_errno(_("could not open '%s'"), git_path_commit_editmsg());
+   if (s->fp == NULL) {
+   int saved_errno = errno;
+   const char *path = git_path_commit_editmsg();
+   errno = saved_errno;
+   die_errno(_("could not open '%s'"), path);
+   }
 
/* Ignore status.displayCommentPrefix: we do need comments in 
COMMIT_EDITMSG. */
old_display_comment_prefix = s->display_comment_prefix;
diff --git a/builtin/init-db.c b/builtin/init-db.c
index c9b7946bad..e384749f73 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -570,9 +570,12 @@ int cmd_init_db(int argc, const char **argv, const char 
*prefix)
set_git_work_tree(work_tree);
else
set_git_work_tree(git_work_tree_cfg);
-   if (access(get_git_work_tree(), X_OK))
-   die_errno (_("Cannot access work tree '%s'"),
-  get_git_work_tree());
+   if (access(get_git_work_tree(), X_OK)) {
+   int saved_errno = errno;
+   const char *path = get_git_work_tree();
+   errno = saved_errno;
+   die_errno(_("Cannot access work tree '%s'"), path);
+   }
}
else {
if (work_tree)
diff --git a/rerere.c b/rerere.c
index 1ce440f4bb..f19a53ff2c 100644
--- a/rerere.c
+++ b/rerere.c
@@ -683,9 +683,12 @@ static int merge(const struct rerere_id *id, const char 
*path)
 * A successful replay of recorded resolution.
 

Re: [PATCH v2 1/3] am: add --show-current-patch

[Junio C Hamano]

Eric Sunshine  writes:

> On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy  
> wrote:
>> Pointing the user to $GIT_DIR/rebase-apply may encourage them to mess
>> around in there, which is not a good thing. With this, the user does
>> not have to keep the path around somewhere (because after a couple of
>> commands, the path may be out of scrollback buffer) when they need to
>> look at the patch.
>>
>> Signed-off-by: Nguyễn Thái Ngọc Duy 
>> ---
>> diff --git a/builtin/am.c b/builtin/am.c
>> @@ -2121,6 +2120,22 @@ static void am_abort(struct am_state *state)
>> +static int show_patch(struct am_state *state)
>> +{
>> +   struct strbuf sb = STRBUF_INIT;
>> +   int len;
>> +
>> +   len = strbuf_read_file(, am_path(state, msgnum(state)), 0);
>> +   if (len < 0)
>> +   die_errno(_("failed to read '%s'"),
>> + am_path(state, msgnum(state)));
>
> Isn't this am_path() invocation inside die_errno() likely to clobber
> the 'errno' from strbuf_read_file() which you want to be reporting?

True.  After coming up with the pathname to the current patch file,
we are going to exit without ever calling am_path(), or underlying
get_pathname() via mkpath(), again before exiting anyway, so perhaps
it is sufficient to just do an am_path() just once upfront, feed it
to strbuf_read_file() and also to die_errno().

Re: [PATCH v2 1/3] am: add --show-current-patch

[Eric Sunshine]

On Wed, Jan 31, 2018 at 4:30 AM, Nguyễn Thái Ngọc Duy  wrote:
> Pointing the user to $GIT_DIR/rebase-apply may encourage them to mess
> around in there, which is not a good thing. With this, the user does
> not have to keep the path around somewhere (because after a couple of
> commands, the path may be out of scrollback buffer) when they need to
> look at the patch.
>
> Signed-off-by: Nguyễn Thái Ngọc Duy 
> ---
> diff --git a/builtin/am.c b/builtin/am.c
> @@ -2121,6 +2120,22 @@ static void am_abort(struct am_state *state)
> +static int show_patch(struct am_state *state)
> +{
> +   struct strbuf sb = STRBUF_INIT;
> +   int len;
> +
> +   len = strbuf_read_file(, am_path(state, msgnum(state)), 0);
> +   if (len < 0)
> +   die_errno(_("failed to read '%s'"),
> + am_path(state, msgnum(state)));

Isn't this am_path() invocation inside die_errno() likely to clobber
the 'errno' from strbuf_read_file() which you want to be reporting?

> +   setup_pager();
> +   write_in_full(1, sb.buf, sb.len);
> +   strbuf_release();
> +   return 0;
> +}